1. Field of the Invention
The present invention relates to a pseudo focal length camera, and more particularly, to the improvement of the view finder optical system thereof.
2. Description of the Related Art
In a camera in which the zoom lens of a photographing optical system is moved by a motor, it is not desirable to rapidly move lenses of the photographing system so that the lenses are stopped precisely at a predetermined position. In this kind of camera, generally, a lens moving speed is set to be low. Consequently, in order to obtain a desired magnification, it takes a long time to move the zoom lens to a proper position. In order to eliminate the disadvantage in performing a zooming operation, the following technique is proposed: The zoom lens is not operated, but an optical system of single focal length is operated to take a photograph. According to the technique, magnetic data for trimming is recorded onto a film so that images within a selected frame are enlarged and printed on a photographic paper according to the trimming data. The technique is hereinafter referred to as a pseudo zoom function. The pseudo zoom function provides a pseudo telescopic photographing effect which is similar to the effect obtained by carrying out a telescopic photographing.
However, in the known camera capable of taking a photograph by the pseudo zoom function, which is referred to as a pseudo focal length camera, the view finder thereof comprises a zoom optical system in which the position of a lens is changed by a motor. Therefore, similar to the drive of the zoom lens of the above-described known photographing optical system, it takes long time to obtain a desired magnification by changing the position of the lens while watching an image in the view finder. When the zoom lens of the view finder optical system is driven to the telescopic side corresponding to increase of magnification in a pseudo telescopic photographing, a photographer is likely to attend to only a principal object. In addition, it takes long to vary the magnification. Therefore, the photographer is apt to forget objects which have moved outside the visual field of the view finder during the increase of magnification. Thus the photographer might take a photograph without including an important object because importance is forgotten during the magnification changing operation.
The above description is concerned with problems caused by a long period of time required for changing the magnification of the image in the view finder. The technique for displaying the shift of the magnification by only enlarging or reducing the frame displayed in the view finder has been developed to solve the above-described problem. According to this technique, the frame corresponding to the pseudo telescopic sight is displayed more narrowly than that corresponding to the pseudo wide angle sight. This technique is able to shift rapidly the frame size and to decide a composition in consideration of the objects positioned outside the frame. But when a photograph is taken on the telescopic side, the frame is greatly reduced. Therefore, the visual field in this case is smaller than that of the view finder comprising the zoom optical system. That is, the visibility of the pseudo telescopic sight is lower than that of the pseudo wide angle sight.
Japanese Patent Laid-Open Publication No. 64-39172 discloses a pseudo focal length camera which takes a photograph using the following technique: An image corresponding to an image which should be printed on a photographic paper is converted into a video signal so as to be stored by a memory. A still picture formed based on the stored signal is enlargedly displayed on a monitor after an exposure. But a photographer can see the image after the exposure.